Oxygen source-oriented control of atmospheric pressure chemical vapor deposition of VO2 for capacitive applications


doi:10.5599/jese.278  165 

 

J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 ; doi: 10.5599/jese.278 

 
Open Access : : ISSN 1847-9286 

www.jESE-online.org 

Original scientific paper 

Oxygen source-oriented control of atmospheric pressure 
chemical vapor deposition of VO2 for capacitive applications 

Dimitra Vernardou*
,
, Antonia Bei**, Dimitris Louloudakis*

,
***,  

Nikolaos Katsarakis*
,
****

,
*****, Emmanouil Koudoumas*

,
***** 

*Center of Materials Technology and Photonics, School of Engineering, Technological Educational 
Institute of Crete, 710 04 Heraklion, Crete, Greece 
**Department of Mechanical Engineering, School of Engineering, Technological Educational Institute 
of Crete, 710 04 Heraklion, Crete, Greece 
***Department of Physics, University of Crete 711 00 Heraklion, Crete, Greece 
****Department of Electrical Engineering, School of Engineering, Technological Educational Institute 
of Crete, 710 04 Heraklion, Crete, Greece 
*****5Institute of Electronic Structure & Laser, Foundation for Research & Technology- Hellas, P.O. 
Box 1527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece. 

Corresponding Author: dvernardou@staff.teicrete.gr  

Received: March 18, 2016; Revised: May 19, 2016; Accepted: May 23, 2016 
 

Abstract 
Vanadium dioxides of different crystalline orientation planes have successfully been 
fabricated by chemical vapor deposition at atmospheric pressure using propanol, etha-
nol and O2 gas as oxygen sources. The thick a-axis textured monoclinic vanadium dioxide 
obtained through propanol presented the best electrochemical response in terms of the 
highest specific discharge capacity of 459 mAh g

-1
 with a capacitance retention of 97 % 

after 1000 scans under constant specific current of 2 A g
-1

. 

Keywords 
Atmospheric pressure chemical vapor deposition; O2 source; Vanadium dioxide; Electrochemical 
properties. 

 

Introduction 

Vanadium dioxide (VO2) exists in more than 10 polymorphs, however, rutile, monoclinic 

(described as a slightly distorted rutile structure) and metastable phases have mainly attracted 

interest because of their interesting chemical and physical properties for catalytic and 

electrochemical applications [1-3]. The crystal structure of VO2 consists of sheets of edge-sharing 

http://www.jese-online.org/
mailto:dvernardou@staff.teicrete.gr


J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 CHEMICAL VAPOR DEPOSITION OF VO2 

166  

VO6 octahedra linked by corner sharing to adjacent sheets along the c-direction of the unit cell [4]. 

This corner-sharing structure strengthens the structural stability and the resistance to lattice 

shearing during cycling in lithium ion batteries [5]. In that context, VO2 was found to show better 

electrochemical performance compared with the well-known V2O5 [6].  

To date, various VO2 forms have been synthesized such as nanocrystalline VO2(B) [4], 

nanothorn VO2(B) hollow microspheres [7], three dimensional hierarchical microflowers and 

microspheres [8,9] as well as VO2/reduced graphene oxide [10,11], VO2(B)/carbon nanotubes [12] 

and hydrogen treated VO2 [13] composite powder materials with sufficient capacitive 

characteristics. But, most of the above mentioned materials showed poor cycling stability after 

500 cycles. Hence, it is important to improve the long-term performance and high rate capability 

of VO2.  

Due to the small compositional differences between numerous phases of vanadium oxides, VO2 

preparation requires a stringent controlled process that provides desired oxygen stoichiometry 

and crystalline structure. In search of such a process, VO2 has been grown using sol-gel [14], 

pulsed laser deposition [15], sputtering [16] and chemical vapor deposition (CVD) [17-20]. Among 

these techniques, CVD at atmospheric pressure (APCVD) is gaining attention because it does not 

require expensive vacuum systems, has fast deposition rates and can be easily integrated to float-

glass production lines [21-24]. A range of precursors have been utilized including vanadium(IV) 

chloride (VCl4) [22], vanadyl(IV) acetylacetonate (VO(acac)2) [23-24], vanadium(V) oxytrichloride 

(VOCl3) [25], vanadium(V) triisopropoxide oxide (VO(OC3H7)3 [26-28]. Since highly oriented VO2 

films exhibited significant variation in conductivity as thermochromic layers [29-31], we were 

inspired to investigate the orientation effect on the APCVD coatings for capacitive applications.  

In this paper, the APCVD of VO2 on SnO2-precoated glass substrate was studied using VO(acac)2 

and propanol, ethanol, O2 gas as oxygen sources from the perspective of the potential application 

of such coatings as cathodes. We have demonstrated the differences in the resulting coatings 

obtained from a structure-orienting role played by the oxygen sources utilized and possible 

explanation of this role is examined. 

Experimental 

Preparation of VO2 coatings 

The APCVD reactor utilized in this work was an in-house design as also reported previously 

[3,23,24]. The vanadium source was the VO(acac)2 (98 %, Sigma-Aldrich), which was placed in a 

bubbler at 200 
o
C, while the gas lines were kept at 220 

o
C to avoid any condensation or blocking. 

The carrier gas was N2 (99.9 %), which was passed through the reactor during all depositions. The 

N2 flow rate through the vanadium precursor bubbler was 1.4 L min
-1

, for growth temperature and 

period of 500 
o
C and 7.5 min, respectively. Additionally, the flow rate of propanol (99.5 %, Sigma-

Aldrich), ethanol (≥ 99.5 %, Sigma-Aldrich) and O2 gas (99.9 %) was 0.8 L min
-1

. Finally, the total N2 

flow rate was kept at 12 L min
-1

 in all CVD experiments. 

The substrates were commercial SnO2-precoated glass (Uniglass, Greece), all of dimensions 

2×2×0.4 cm. Prior to deposition, they were all cleaned with H2O and detergent, rinsed thoroughly 

with H2O and deionised H2O, and allowed to dry in air. Once the allotted time was complete, the 

reactor temperature was turned off and the substrate allowed cooling at 100 
o
C under an 

atmosphere of N2. Then it was removed from the reactor, handled and stored in air. 
 



D. Vernardou et al. J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 

doi:10.5599/jese.278 167 

Structural and morphological characterization of coatings 

The structure of the coatings was examined in a Siemens D5000 Diffractometer for 2-theta = 

15.00 – 60.00 
o
, step size 0.05 

o
 and step time 5 min/

o
. Additionally, their morphology was 

evaluated in a Jeol JSM-7000 microscope. In this case, coatings were over-coated with a thin film 

of gold prior to analysis to avoid charging. 

Finally, the coating’s thickness was estimated using a profilometer A-step TENCOR. A step was 

done by etching the vanadium oxide coatings off the SnO2-precoated glass substrate in 1:3, 

H2O2 (30 %):HCl. Tin dioxide remained intact after this procedure and the thickness was obtained 

from the measured step height. 

Electrochemical evaluation  

Cyclic voltammetry experiments were performed using a three electrode electrochemical cell as 

reported previously [32-34] for a potential range of -1 V to +1 V, a scan rate of 10 mV s
-1

 and a 

number of scans up to 1000. In particular, Pt, Ag/AgCl and vanadium oxides on SnO2-precoated 

glass substrates were used as counter, reference and working electrodes, respectively. All measu-

rements were carried out in 1 M LiOH, which acted as electrolyte. The chronoamperometric mea-

surements were done at -1 V and +1 V for a step of 200 s and a total period of 2000 s. Additionally, 

the chronopotentiometric curves were obtained at a constant specific current of 2 A g
-1

 and a 

potential range of +0.1 V to +0.6 V.  

Results and discussion 

Presented here are investigations into APCVD VO2 coatings grown from VO(acac)2 and three 

oxygen sources: propanol, ethanol and O2 gas. It will be shown that a level of control can be 

exerted over orientation and morphology through the different sources. All coatings produced 

were stable in air for over six months and resistant to H2O, acetone and toluene. Additionally, they 

passed the “scotch tape test”; a piece of sticky tape was placed on the coating and then removed 

without lifting off the coating. 

Structure 

Figure 1 presents the x-ray diffraction (XRD) patterns of the APCVD coatings using propanol, 

ethanol and O2 gas. As shown in the case of propanol and ethanol, one diffraction peak is observed 

at 18.21 
o
, which matches to monoclinic a-axis textured VO2 coatings [30,31,35]. This peak can be 

indexed to 100 plane showing the preferred orientation growth of these coatings. Furthermore, 

the XRD pattern of the as-grown coatings using O2 gas show two peaks at 55.4 and 57.6 
o
 with 

Miller indices 022 and 220 due to monoclinic VO2 phase indicating that is a 022-oriented single 

phase [36-38]. Finally, peaks at 26.5, 33.7, 37.1, 51.7 and 54.7 
o
 with respective Miller indices 110, 

101, 211 and 220 (indicated with asterisk in Figure 1) are due to SnO2–precoated glass substra-

te [39]. The preferential orientation of the VO2 on SnO2-precoated glass substrates at angles other 

than 27.8 
o
 is not clearly understood. Nevertheless, it seems to be more sensitive to O2 source 

during the growth rather than to glass substrate. The reaction mechanism for the formation of VO2 

from VO(acac)2 in the presence of O2 gas has previously been studied in the literature [40]. The 

possible decomposition routes of VO(acac)2 species involve a simple intramolecular 

rearrangement of the VO(acac)2 precursor resulting in the release of two C3H4 molecules, followed 

by the decomposition of VO(CH3COO)2 to yield (CH3CO)2O and VO2. On the other hand, in the case 

of alcohols, the VO2 deposits possibly act as heterogeneous catalytic sites for their oxidation to 

propanal (for propanol) and acetaldehyde (for ethanol). A similar behavior is also observed in the 



J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 CHEMICAL VAPOR DEPOSITION OF VO2 

168  

presence of methanol [41,42]. The active oxygen required for their oxidation comes from the 

VO(acac)2 itself, since it can be regarded as a source of excess oxygen (there are 5 oxygen atoms to 

1 V atom, while only 2 oxygen atoms are required for VO2 formation). 

Other researchers have also attempted to control the crystalline orientation of VO2. Gary et. al. 

reported the a-axis textured VO2 deposited on R-plane sapphire and suggested that the cause 

could be a stress developing on the interface between the substrate and the coating [30]. 

Muraoka et. al. studied the epitaxial growth of VO2 001-oriented single phase on TiO2 001 

substrates and 110-oriented phase on TiO2 110, respectively [29]. Ngom et. al. indicated that the 

crystalline orientation of the VO2 thin films was drastically changed because of the formation of an 

interface layer between the VO2 and the soda lime glass [35]. Chiu et. al. also attempted to grow 

VO2 on glass using a 5 nm ZnO buffer layer. In the case of the direct VO2 growth on amorphous 

glass, polycrystalline films formed, while only VO2 011 peaks located at 27.90 
o
 were observed for 

the growth on ZnO [43].   
 

 

Figure 1. XRD of APCVD vanadium oxides at 500 
o
C for 0.8 L min

-1
 flow rate of propanol, ethanol and O2 gas. 

Morphology 

Figure 2 presents the field-emission scanning electron microscope (FE-SEM) images of 

vanadium oxide coatings grown at 500 
o
C on SnO2-precoated glass substrate for 0.8 L min

-1
 flow 

rate of propanol, ethanol and O2 gas. For propanol and ethanol, compact grains of nearly round 

shape are mainly observed with their sizes being 160 nm and 40 nm, respectively. It was observed 

that thinner coatings grown using ethanol (95 nm) were denser, while as thickness increased for 

propanol (120 nm), the surface appeared less dense with growth at specific sites, suggestive of a 

Stranski-Krastanov type of growth mechanism [44]. Regarding the O2 gas, agglomeration of grains 

forming rod-like structures is shown with thickness of 80 nm. 



D. Vernardou et al. J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 

doi:10.5599/jese.278 169 

 
Figure 2. FE-SEM of APCVD vanadium oxides at 500 

o
C for 0.8 L min

-1
 flow rate of propanol (a), 

ethanol (b) and O2 gas (c). 

Electrochemical characteristics 

In order to study the effect of oxygen source on the electrochemical performance of the 

coatings, cyclic voltammetry curves were obtained as indicated in Figure 3. The potential range 

was -1 V to +1 V at a scan rate of 10 mV s
-1

. All curves are normalized to the mass of the working 

electrode. The mass was measured by a 5-digit analytical grade scale and found to be 0.00002 g, 

which was obtained by measuring the glass substrate before and after the growth. It can be 

observed that the as-grown vanadium oxide coatings using propanol present two anodic peaks at -

0.05 V / +0.52 V and two cathodic peaks at -0.15 V / ≈+0.64 V (vs. Ag/AgCl), which are 

accompanied by color changes from green, blue to yellow and then yellow, blue to green. Since, 

the electrochemical cell is made up of glass, we have observed these color changes during the 

measurements. One may then assume that V
+5

 ions are reduced to V
+4

 and V
+3

, since two anodic 

peaks are observed. A similar explanation can be given for the oxidation peaks, i.e. V
+3

 ions oxidize 

into V
+4

 and V
+5

. These color changes are attributed to Li
+
 intercalation and deintercalation [45]. 

On the other hand, the shape of the curve for the vanadium oxide coating using O2 gas is different 

indicating one anodic peak at +0.11 V and one cathodic peak at -0.34 V accompanied by color 

changes from green to yellow and vice versa. This may be due to the existence of different VO2 



J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 CHEMICAL VAPOR DEPOSITION OF VO2 

170  

orientation planes compared with the one observed for alcohols. Furthermore, the specific current 

of the as-grown coatings using alcohols as oxygen source is the highest presenting an enhanced 

electrochemical activity. We then suggest that this is correlated to both the 100 plane and the 

increased thickness, which incorporate more active material for the insertion of Li
+
.  

 

Figure 3. Cyclic voltammograms of the first scan for the APCVD vanadium oxide coatings  
for 0.8 L min

-1
 flow rate of propanol, ethanol and O2 gas and an electrode geometrical active area  

of 1 cm
2
. Maximized cyclic voltammogram curve for the region of -0.2 V - +1 V of the  

grown vanadium oxide coating using propanol as inset. 

Chronoamperometry measurements were also performed to calculate the specific charge 

during Li
+
 intercalation / deintercalation. It is estimated by integration of excess current measured 

upon switching the bias potential with time [32] as shown in Figure 4 for the as-grown vanadium 

oxide using 0.8 L min
-1

 of propanol. The amount of specific charge for propanol found to be 

120 C g
-1

, which is three times higher than that of O2 gas. 

 
Figure 4. The chronoamperometric response of the first scan recorded at -1 V and +1 V for an 

interval of 200 s of the as-grown coatings at 500 
o
C for 0.8 L min

-1
 flow rate of propanol. 



D. Vernardou et al. J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 

doi:10.5599/jese.278 171 

 
Figure 5. Intercalated and deintercalated specific charge as a function with oxygen source utilized. 

Figure 6 presents the specific discharge capacities of the as-grown coatings at 500 
o
C for 7.5 in 

using 0.8 L min
-1

 flow rate of propanol, ethanol and O2 gas under a constant specific current of 

2 A g
-1

. The propanol’s curve indicates two plateaus at approximately 0.25 V and 0.5 V, which 

present the two-step Li
+
 intercalation process as also observed in cyclic voltammetry analysis. The 

specific discharge capacity was 459 mAh g
-1

 with a capacitance retention of 97 % after 1000 scans 

(Figure 6 inset) keeping the staircase shape, which is promising for lithium ion batteries. The speci-

fic discharge capacity was higher than the APCVD metastable [3] and 022-oriented monoclinic VO2 

[24]. On the other hand, the ethanol and O2 gas samples lack of staircase-like shape probably due 

to the less defined phase transition associated with Li
+
. This result may arise due to the largest 

thickness of the propanol sample, which facilitates larger number of Li
+
 within the vanadium oxide 

lattice. 

 
Figure 6. The chronopotentiometric curves for the as-grown sample at 500 

o
C for 7.5 min using 0.8 L min

-1
 

propanol, ethanol and O2 gas under a constant specific current of 2 A g
-1

 and potential ranging from 0.1 V to 
0.6 V. The 1000

th
 scan of 0.8 L min

-1
 propanol is also included as inset. 



J. Electrochem. Sci. Eng. 6(2) (2016) 165-173 CHEMICAL VAPOR DEPOSITION OF VO2 

172  

Conclusions 

Vanadium dioxides of different crystalline orientation were grown by APCVD at 500 
o
C for 

7.5 min using propanol, ethanol and O2 gas. The a-axis textured monoclinic was enhanced with 

propanol and ethanol, while the 022-oriented single phase VO2 was obtained with O2 gas. Conse-

quently, the samples with different orientations possessed different morphologies; a-axis textured 

coatings showed grains, while the 022-oriented phases presented agglomeration of grains forming 

rod-like structures. Electrochemical analysis has shown that the a-axis textured monoclinic VO2 
grown using propanol has several unique characteristics compared with the rest of the samples, 

which makes it promising electrode material for lithium ion batteries. These include the thickness, 

which facilitates Li
+ 

access to a large volume of active material and the specific discharge capacity 

of 459 mAh g
-1

 with capacitance retention of 97 % after 1000 scans under constant specific current 

of 2 A g
-1

 indicating both high rate performance and good stability. 

 
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